This invention relates to chiral materials and their use as doping, agents for liquid crystals for a wide range of applications including solid state cholesteric filters for projection displays, circular polariser, optical filter. etc.
The addition of a chiral compound to an achiral liquid crystalline phase is one of the procedures currently used for the conversion of achiral into chiral mesophases. The nematic phase, for example, is converted to the cholesteric one when being doped with a small amount of a chiral substance. This conversion manifests itself by the occurrence of an intermolecular helix which is characterised by the-so-called helical twisting power (HTP) given in Equation 1.                               HTP          =                                                                      [                                                            ⅆ                                              p                                                  -                          1                                                                                                            ⅆ                      x                                                        ]                                                  X                  =                  0                                            ≅                                                p                                      -                    1                                                  x                                      =                                          ∑                i                            ⁢                                                                    x                    i                                    ⁡                                      (                    HTP                    )                                                  i                                                    ⁢                  
                ⁢                                                            HTP                ⁢                                  xe2x80x83                                ⁢                                  (                                      µm                                          -                      1                                                        )                                                                                    helical                ⁢                                  xe2x80x83                                ⁢                twisting                ⁢                                  xe2x80x83                                ⁢                power                ⁢                                  xe2x80x83                                ⁢                for                ⁢                                  xe2x80x83                                ⁢                small                ⁢                                  xe2x80x83                                ⁢                concentrations                                                                                        p                ⁢                                  xe2x80x83                                ⁢                                  (                  µm                  )                                                                                                      pitch                  ⁢                                      xe2x80x83                                    ⁢                  of                  ⁢                                      xe2x80x83                                    ⁢                  induced                  ⁢                                      xe2x80x83                                    ⁢                  helix                                ,                                  xe2x80x83                                ⁢                                                      +                                          xe2x80x83                                        ⁢                    for                                    ⁢                                      xe2x80x83                                    ⁢                                      (                    P                    )                                    ⁢                                      -                                                  ,                                  xe2x80x83                                ⁢                                                      -                                          xe2x80x83                                        ⁢                                          for                      ⁢                                              xe2x80x83                                            ⁢                                              
                                            (                      M                      )                                                        ⁢                                      -                                    ⁢                  helix                                                                                        x                                                      mole                ⁢                                  xe2x80x83                                ⁢                fraction                ⁢                                  xe2x80x83                                ⁢                of                ⁢                                  xe2x80x83                                ⁢                the                ⁢                                  xe2x80x83                                ⁢                dopant                                                                                        ∑                i                                                                    sum                ⁢                                  xe2x80x83                                ⁢                over                ⁢                                  xe2x80x83                                ⁢                all                ⁢                                  xe2x80x83                                ⁢                chiral                ⁢                                  xe2x80x83                                ⁢                conformers                ⁢                                  xe2x80x83                                ⁢                of                ⁢                                  xe2x80x83                                ⁢                the                ⁢                                  xe2x80x83                                ⁢                dopant                                                                                        x                i                                                                    mole                ⁢                                  xe2x80x83                                ⁢                fraction                ⁢                                  xe2x80x83                                ⁢                of                ⁢                                  xe2x80x83                                ⁢                conformer                ⁢                                  xe2x80x83                                ⁢                i                                                                        (        1        )            
Said HTP is in fact a measure for the efficiency of a given dopant and is determined by the Cano method with solutions of the dopant in the host mesophase. Since the chiral guest and the achiral host compounds are not necessarily compatible at the molecular scale, their binary solution is frequently characterised by undesirable chances of the thermotropic sequence of the initial host liquid crystalline material, like for example a depression of the clearing point. Those changes could in turn have negative effects on the phase properties of the host, such as a decrease of the birefringence etc. Therefore, a chiral dopant is sought so that with very small concentrations of this latter, large values of HTP could be induced.
As such efficient chiral dopants there are the binaphthol derivatives described in GB-A-2 298 202. However chiral binaphthol derivatives may undergo partial racemisation when being heated. Besides, their preparation is expensive because it includes asymmetric resolution of binaphthol racemate as a crucial reaction step.
U.S. Pat. No. 4,835,277 (Choe / Hoechst Celanese Corporation) discloses at Example 1 a polymer of L-N-p-nitrophenyl-2-pyrrolidinemethyl acrylate: 
Synthetic Metals 57 (1), 1993, 3945-3950 (Feng et al.) discloses compounds of the following formula: 
The above two documents are in the field of polymer films showing non-linear optical properties. In unrelated fields the following may be mentioned:
xe2x97xaf Tet. Lett. 27 (36), 1986, 4303-4306 (Calmes et al.) disclosing a compound of the following formula: 
xe2x97xaf Bull. Chem. Soc. Jpn. 60 (11), 1987, 4190-4192 (Kawanami et aL) disclosing what would appear to be a compound of the following formula: 
xe2x97xaf J. Org. Chem. 57, 1992, 1179-1190 (Goldstein et al.) disclosing a compound of the following formula, an enol ether intermediate in a route for the synthesis of amphibian alkaloids: 
The synthesis of chiral compounds bearing a carbon atom as a single asymmetric chiral centre is generally trivial and inexpensive. Nevertheless, their use as doping agents for liquid crystals has only provided mixtures with a relatively small HTP. However, we have now discovered that a further class of compounds, including within its scope compounds that exhibit a sterically hindered single chiral centre, is efficient for producing a large HTP.
Thus the invention provides chiral prolinol derivatives of formula 1: 
in which:
A1, A2 and A4 each independently represents hydrogen; an optionally-substituted methyl group; an optionally-substituted aliphatic group with 2 to 80 C-atoms, in which one or more C-atoms may be replaced by a heteroatom, in such a manner that oxygen atoms are not linked directly to one another; or an optionally-substituted aromatic ring system, with 1 to 80 C-atoms; and
A3 represents an optionally-substituted aliphatic group with 2 to 80 C-atoms, in which one or more C-atoms may be replaced by a heteroatom, in such a manner that oxygen atoms are not linked directly to one another; or an optionally-substituted aromatic ring system, with 1 to 80 C-atoms;
wherein at least one of the A1 to A4 residues includes a polymerisable group, with the proviso that, when the only polymerisable group is in the A3 residue, the polymerisable group does not comprise a double bond directly connected to the carbon atom linking A3 and A4.
The term xe2x80x9caliphaticxe2x80x9d includes straight-chain and branched alkyl, as well as saturated and unsaturated groups. Possible substituents include alkyl, aryl (thus giving an araliphatic group) and cycloalkyl, as well as amino, cyano, epoxy, halogen, hydroxy, nitro, oxo etc. Possible heteroatoms which may replace carbon atoms include nitrogen, oxygen and sulphur. In the case of nitrogen further substitution is possible with groups such as alkyl, aryl and cycloalkyl.
The compounds of the invention have surprisingly been found to be efficient for producing a large HTP, even those that exhibit a single chiral centre. Of course, other chiral groups may be present elsewhere in the molecule.
The compounds of the invention may be used as doping agents for liquid crystals for a wide range of applications including solid state cholesteric filters for projection displays, circular polariser, optical filter, etc.
Note that, although one or more of A1, A2 and A4 may independently represent hydrogen or an optionally-substituted methyl group, A3 always represents a bulkier optionally-substituted aliphatic group with 2 to 80 C-atoms, in which one or more C-atoms may be replaced by a heteroatom, or an optionally-substituted aromatic ring system. Thus at least one such bulkier group is always present in the compounds of the invention. Although one or both of A1 and A4 may represent a small group such as hydrogen or methyl, it is preferable to have several bulky groups. Thus, preferably A1, A3 and A4 each independently represents an optionally-substituted aliphatic group with 2 to 80 C-atoms, in which one or more C-atoms, may be replaced by a heteroatom, in such a manner that oxygen atoms are not linked directly to one another; or an optionally-substituted aromatic ring system, with 1 to 80 C-atoms.
Preferred embodiments of the invention relates to chiral prolinol derivatives of formula I. wherein:
A3 and A4 have each independently one of the meanings of formula II:
xe2x80x94X1xe2x80x94(Sp1)nxe2x80x94X2xe2x80x94(MG)xe2x80x94X3xe2x80x94(Sp2)mxe2x80x94Pxe2x80x83xe2x80x83(II)
A2 is a hydrogen atom or has one of the meanings of formula IIb or one of the meanings of formula IIc: and
A1 has one of the meanings of formula IIb or one of the meanings of formula IIc:
xe2x80x94(Sp1)nxe2x80x94X2xe2x80x94(MG)xe2x80x94X3xe2x80x94(Sp2)mxe2x80x94Pxe2x80x83xe2x80x83(IIb)
xe2x80x94(Sp1)nxe2x80x94X2xe2x80x94(MG)xe2x80x94X4xe2x80x83xe2x80x83(IIc)
in which:
X1 to X3 each independently denote xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94N(CH3)xe2x80x94, xe2x80x94CH(OH)xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94CH2(CO)xe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94CH2(SO)xe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94CH2(SO2)xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94OCOxe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Sxe2x80x94, xe2x80x94SOOxe2x80x94, xe2x80x94OSOxe2x80x94, xe2x80x94SOSxe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94C(H=CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 or a single bond;
X4 is a halogen;
Sp1and Sp2 are each independently straight or branched spacer groups having 1 to 20 C-atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more CH2 groups to be replaced, in each case independently from one another, by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94N(CH3)xe2x80x94, xe2x80x94CH(OH)xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94CH2(CO)xe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94CH2(SO)xe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94CH2(SO2)xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94OCOxe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Sxe2x80x94, xe2x80x94SOOxe2x80x94, xe2x80x94OSOxe2x80x94, xe2x80x94SOSxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94(Si(CH3)2O)q1xe2x80x94, xe2x80x94(CF2)xe2x80x94r, xe2x80x94(CD2)sxe2x80x94 or xe2x80x94C(W1)=C(W2)xe2x80x94, in such a manner that oxygen atoms are not linked directly to one another, with q1, r and s in the range 1 to 15: and W1 and W2 each independently denote H. Hxe2x80x94(CH2)q2xe2x80x94 or C1 with q2 in the range 1 to 15:
P is a polymerisable group selected from the formulae: CH2=CWxe2x80x94, CH2=CWxe2x80x94COOxe2x80x94, CH2=C(Ph)xe2x80x94COOxe2x80x94, CH2=CHxe2x80x94COOxe2x80x94Phxe2x80x94, CH2=CWxe2x80x94COxe2x80x94NHxe2x80x94, CH2=C(Ph)xe2x80x94CONHxe2x80x94, CH2=C(COOR1)xe2x80x94CH2xe2x80x94COOxe2x80x94, CH2=CHxe2x80x94Oxe2x80x94, CH2=CHxe2x80x94OOCxe2x80x94, Phxe2x80x94CH=CHxe2x80x94, CH3xe2x80x94C=Nxe2x80x94(CH2)m3xe2x80x94, HOxe2x80x94, HSxe2x80x94, HOxe2x80x94(CH2)m3xe2x80x94, HSxe2x80x94(CH2)m3xe2x80x94, HO(CH2)m3COOxe2x80x94, HS(CH2)m3COOxe2x80x94, HWNxe2x80x94, HOC(O)xe2x80x94, CH2=CHxe2x80x94Phxe2x80x94(O)m4, 
with W being H, C1 or alkyl with 1-5 C atoms, m3 being 1-9, m4 being 0 or 1, Ph being phenyl, Rxe2x80x2 being alkyl with 1-5 C atoms, Rxe2x80x3 having the meaning of Rxe2x80x2 or being methoxy, cyano or a halogen;
n and m are each independently in the range 0 to 4; with the proviso that when n is 0, then X1 is a single bond; and when m is 0, then X3 is a single bond; and
MG is a mesogenic group comprising 1 to 4 aromatic or non-aromatic carbocyclic or heterocyclic ring systems and optionally up to 3 bridging groups and preferred are those selected each independently from the meanings of formulae III:
C1"Parenopenst"Z1xe2x88x92C2)a1"Parenopenst"Z2xe2x88x92C3)a2"Parenopenst"Z3xe2x88x92C4)a3xe2x80x83xe2x80x83(III),
in which:
C1 to C4 are in each case independently optionally substituted non-aromatic, aromatic, carbocyclic or heterocyclic groups, and are in preferred embodiments those selected from the formulae: 
with:
L being xe2x80x94CH3, xe2x80x94COCH3, xe2x80x94NO2, CN, or halogen;
u1 being 0, 1, 2, 3, or 4;
u2 being 0, 1, 2, or 3;
u3 being 0, 1, or 2:
Z1 to Z3 are independently from each other xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94CH=CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94CH=CHxe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94CH=CHxe2x80x94 or a single bond; and
a1, a2 and a3 are independently integers from 0 to 3, such that a1xe2x88x92a2+a3xe2x89xa64.
We have discovered that, to attain high values of HTP for a given guest-host liquid-crystalline system, it is desirable to increase the size and the conformational stability of the substituents around the chiral centre of the optically active host molecule. It is possible to realise such a strategy in the present invention with chiral prolinol derivatives of formula I where the two xcex1 positions could be derivatised with bulky A3 and A4 substituents starting, for example, from the Grignard analogues of A3 and A4 of appropriate structure selected from the formula II and proline methyl ester hydrochloride, commercially available in both L and D enantiomeric forms.
The generated hydroxy group could be then derivatised, using classical synthetic methods with A1 appropriately selected from the formula IIb as organic residue, permitting the increase of solubility and/or the increase of compatibility of 1 with the guest liquid crystalline systems.
More preferred embodiments of the present invention are:
a) Chiral prolinol derivatives of formula I wherein A3 and A4 are identical: and
b) Chiral prolinol derivatives of formula I wherein A2 has one of the meanings of formula IV:
(Sp2)m4xe2x80x94(O)m5xe2x80x94P2 xe2x80x83xe2x80x83(IV),
A3 and A4, have one of the meanings of formula V.
xe2x80x94MGxe2x80x94X3xe2x80x94(Sp2)m4xe2x80x94P3xe2x80x83xe2x80x83(V)
and A1 has one of the meanings of formula Va:
xe2x80x83xe2x80x94MGxe2x80x94X3xe2x80x94(Sp2)m4xe2x80x94P4xe2x80x83xe2x80x83(Va).
in which:
Sp2 is alkylene with 0 to 20 C-atoms;
P2 is H, CH2=CW5xe2x80x94 or CH2=CW5xe2x80x94COxe2x80x94;
P3 is H, CH2=CW5xe2x80x94, CH2=CW5xe2x80x94COOxe2x80x94, W5CH=CHxe2x80x94Oxe2x80x94 or CH2=CW5xe2x80x94Oxe2x80x94;
P4 is CH2=CW5xe2x80x94, CH2=CW5xe2x80x94COOxe2x80x94, W5CH=CHxe2x80x94Oxe2x80x94 or CH2=CW5xe2x80x94Oxe2x80x94; with W5 being H, CH3, or C1;
m4 and m5 are each independently 0 or 1 in such a manner that oxygen atoms are not linked directly to one another;
MG has the meaning given for C1; and
X3 is xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94CH=CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94CH=CHxe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94CH=CHxe2x80x94 or a single bond.
Preferred compounds of formula I are those for which A2 has one of the meanings of formula IV and A3 and A4 have one of the meanings of formula V and A1 has one of the meanings of formula Va, in which:
MG is phenylene, biphenylene. naphthylene or phenanthrylene;
X3 denotes xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, or a single bond, in particular, xe2x80x94Oxe2x80x94, or a single bond;
Sp2 is straiht-chain of formula xe2x80x94(CH2)vxe2x80x94 with v being an integer between 0 and 20, especially preferred is ethylene, propylene. butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, or dodecylene;
P2 is H, CH2=CW5xe2x80x94 or CH2=CW5xe2x80x94COxe2x80x94;
P3 is H, CH2=CW5xe2x80x94, CH2=CW5xe2x80x94COOxe2x80x94, W5CH=CHxe2x80x94Oxe2x80x94 or CH2=CW5xe2x80x94Oxe2x80x94;
P4 is CH2=CW5xe2x80x94, CH2=CW5xe2x80x94COOxe2x80x94, W5CH=CHxe2x80x94Oxe2x80x94 or CH2=CW5xe2x80x94Oxe2x80x94; with W5 being H, CH3, or C1; and
m4 and m5 are each independently 0 or 1 in such a manner that oxygen atoms are not linked directly to one another.
When the only polymerisable group is in the A3 residue, the polymerisable group does not comprise a double bond directly connected to the carbon atom linking A3 and A4. However, preferred compounds of formula I are those in which, when the only polymerisable group is in either the A3 or the A4 residue, the polymerisable group does not comprise a double bond directly connected to the carbon atom linking A3 and A4.
Other aspects of the present invention are:
a) a liquid crystalline material, especially in the form of a liquid crystalline mixture. (co)polymer, elastomer, polymer gel or polymer network comprising at least two components, at least one of which is a chiral compound, characterised in that the chiral compound is a prolinol derivative of formula I;
b) a liquid crystalline material, especially in the form of a cholesteric mixture, or cholesteric polymer network, comprising at least two components, at least one of which is a chiral compound, characterised in that the chiral compound is a prolinol derivative of formula I;
c) a cholesteric polymer network obtainable by copolymerisation of an optically active polymerisable mesogenic mixture comprising:
i) at least one chiral or/and achiral nematic polymerisable mixture chosen from the already reported broad range of chiral and achiral nematic materials, for example in Adv. Mater. 5, 107 (1993), Mol. Cryst. Liq. Cryst. 307, 111 (1997), J. Mat. Chem. 5, 2047 (1995) or in patent applications U.S. Pat. No. 5,593,617; U.S. Pat. No. 5,567,349; GB-A-2297556; GB-A-2299333; DE-A-19504224;
EP-A-0606940; EP-A-0643121 and EP-A-0606939, optionally selected from EP-A-0606940; EP-A-0643121 and EP-A-06069399;
ii) at least one chiral dopant of formula I;
iii) an initiator;
iv) optionally a non-mesogenic compound having at least one polymerisable functional group, more optionally a diacrylate compound; and
v) optionally a stabiliser:
e) chiral polymerisable cholesteric mixtures, essentially consisting of:
i) 70 to 99% preferably 85 to 95% by weight of at least one achiral polymerisable liquid crystal.
ii) 0.1 to 30%, preferably 1 to 15% by weight of a chiral compound of formula I;
iii) 0.1 to 5%. preferably 0.2 to 2% by weight of a photoinitiator; and
iv) 0 to 5%, preferably 0.1 to 1% of a stabiliser; and
f) a cholesteric film obtainable by the steps comprising ordering the above mixture in the monomeric state and in situ UV polymerisation of the resulting ordered mixture.
The inventive chiral compounds disclosed in the foregoing and the following can be prepared by methods which are known per se and which are described in standard works of organic chemistry such as, for example, Houben-Weyl, Methoden der Organischen Chenie, Thieme-Verllag, Stuttgart. In the present case of compounds I the commercially available L-proline methyl ester is used as starting material, for example according to the following reaction schemes: 
According to the synthetic ways drawn in Schemes 1-3, typical examples representing polymerisable chiral prolinol derivatives shown in the following list of compounds mav be prepared. This list is, however, to be understood only as illustrative without limiting the scope of the present invention: 
Different methods can be used for the formation of the desired cholesteric network, starting from the polymerisable coloured cholesteric mixture manufactured as described above. Preferably, transparent substrates, optionally ITO (indium tin oxide) coated, and more preferably glass or plastic substrates, were used. Said substrates carried a layer of rubbed polyimide or polyamide or a layer of coated photopolymer. Said layers are used to orient the molecular helix which forms spontaneously in the cholesteric mixture. To preclude the formation of disclinations, the polymerisable cholesteric mixture was:
coated into a thin film, or
provided between two of the said substrates which were sheared over a small distance until a planar order was obtained, or
capillary filled between two of the said substrates,
then subsequently cured, for example, by UV light, preferably in the presence of a photoinitiator, for example, an IRGACURE(trademark). Due to the strength of the three-dimensional polymer network thus formed, the film may be peeled off and used, for example, as a self-supporting cholesteric polariser.
The reflected colour from the formed cholesteric layer is dependent on the pitch length of the cholesteric helix, said pitch length being itself dependent on the concentration of the chiral dopant in, for example a nematic host. For small and high concentrations of the chiral dopant, the cholesteric network reflects red and blue colours respectively.
The novel chiral prolinol derivatives of formula I are highly suitable for producing cholesteric films which can be used in different optical and electro-optical applications.